Ok, regarding the Duplicatus spell, how does it work in combat? Suppose a caster conjurs 4 duplicates how would that affect the casters chance to be hit in melee combat, ranged combat and with spells? How do you calculate it?

Was there ever any official errata or ruling on this, either in German or English?

That’s true, the “Dodge 16” is what you have even if you were otherwise unable to parry/dodge (Onslaught, attack of opportunity)If you do have a parry of 10 (already not too bad) 4 duplicates would effectively give you the equivalent of 18 or less on d20 to defend. And 3 duplicates (QL 4, possible at start of game) is almost as good, 87.5% instead of 90% in the example above.